1. Field of the Invention
This invention relates to a fan motor driving circuit and more particularly to a driving circuit for a brushless fan motor.
2. Description of the Prior Art
FIG. 6 shows a conventional driving circuit for a DC brushless fan motor having coils separated by 180 degrees from each other to form a two-phase winding. Reference numerals 1 and 2 denote bias resistors for a hall element 3 for detecting a magnetic pole position of a rotor magnet, 4 denotes a differential amplifier for amplifying an output of the hall element 3, 5 denotes a conducting current signal generating circuit for receiving an output of the differential amplifier 4 and a signal from a rotary speed varying means 30, and generating a conducting current signal other than conducting current signals of two phases separated by 180xc2x0 from each other, 6 and 7 denote buffer resistors, 8 and 9 denotes transistors which receive outputs of the conducting current signal generating circuit 5 and are conducted alternately, and 10 and 11 denote stator windings.
The rotary speed varying means 30 is composed of a rotary pulse generating circuit 31, a time constant circuit 40, a comparator 34, and a rotary speed instructing means 91 composed of a resistor 33 and a variable resistor 32.
The time constant circuit 40 is composed of a resistor 41, a capacitor 42, and a transistor 43. The rotary speed varying means 30 shapes the output of the differential amplifier 4 into a signal in a shape of rectangular wave and then generates a discharge pulse during a short period of time. The time constant circuit 40 generates a voltage of saw tooth wave form across the capacitor 42 according to a time constant determined by the resistor 41 and the capacitor 42. This voltage is divided by the resistors 32 and 33. The comparator 34 operates the conducting current signal generating circuit 5 to energize the stator windings 10 and 11, when the divided voltage reaches a reference voltage. That is, the conducting current signal generating circuit 5 interrupts the conducting current during a predetermined period of time, when an output of the hall element 3 is generated, so that an effective conducting current is reduced, and that the rotary speed of the fan motor is controlled according to the current interruption time.
In the conventional driving circuit, however, the rotary speed of the fan motor is varied according to the voltage variation of the power source, because no feedback circuit of the rotary speed of the motor is provided, though it is possible to vary the rotary speed of the motor by the variable resistor 32 of the rotary speed instructing means 91.
The power consumption is increased in proportion to the square of the rotor speed, the temperature becomes high, and the noise is increased remarkably, especially when the voltage of the power source is elevated over the rated voltage.
In order to solve the above problems, it is considered to control the variation of the rotary speed by the speed feed back, however, the circuit becomes complicated and the space and the cost for installing the electronic parts are increased.
An object of the invention is to provide a fan motor driving circuit which solves the above problems.
Another object of the present invention is to provide a fan motor driving circuit comprising means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a predetermined rated voltage when the power source voltage is elevated over the rated voltage, and means for controlling a rotary speed of a fan motor to a predetermined value by varying an elementary signal for determining the rotary speed of the fan motor according to an output voltage of the power source voltage detecting means automatically when the power source voltage is elevated over a predetermined value.
A further object of the present invention is to provide a brushless fan motor driving circuit comprising means for detecting a position of a permanent magnet of a rotor, a conducting current signal generating circuit for generating a conducting current signal according to an output of the position detecting means, a conducting current control element for energizing stator windings of the motor according to the conducting current signal, means for varying a rotary speed of a fan motor, means for generating a rotary speed instructing voltage, means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a rated voltage when the power source voltage is elevated over a predetermined rated voltage, and means for controlling a rotary speed of a fan motor to a predetermined value by varying the rotary speed instructing voltage by an output voltage of the power source voltage detecting means automatically when the power source voltage is elevated over the predetermined rated voltage, the rotary speed varying means comparing a saw-tooth wave signal generated in a saw-tooth wave generating circuit including a time constant circuit consisting of a resistor and a capacitor with the rotary speed instructing voltage so as to vary an energizing time of the stator windings.
Yet further object of the present invention is to provide a brushless fan motor driving circuit comprising means for detecting a position of a permanent magnet of a rotor, a conducting current signal generating circuit for generating a conducting current signal according to an output of the position detecting means, a conducting current control element for energizing stator windings of the motor according to the conducting current signal, means for varying a rotary speed of a fan motor, the rotary speed varying means comparing a saw-tooth wave signal generated in a saw-tooth wave generating circuit including a time constant circuit consisting of a resistor and a capacitor with the rotary speed varying voltage so as to vary an energizing time of the stator windings, means for generating a rotary speed instructing voltage for setting a rotary speed of a brushless fan motor to a predetermined value, means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a rated voltage when the power source voltage is elevated over a predetermined rated voltage, and means for controlling a rotary speed of the fan motor to a predetermined value by varying an inclined angle of the saw-tooth wave of the rotary speed varying means according to an output voltage of the power source voltage detecting means automatically when the power source voltage is elevated over the predetermined rated voltage.
A still further object of the present invention is to provide a brushless fan motor driving circuit comprising means for detecting a position of a permanent magnet of a rotor, a conducting current signal generating circuit for generating a conducting current signal according to an output of the position detecting means, a conducting current control element for energizing stator windings of the motor according to the conducting current signal, means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a rated voltage when the power source voltage is elevated over a predetermined rated voltage, means for detecting a current from the conducting current control element, a comparator for comparing an output of the conducting current detecting means with an output of the power source voltage detecting means, and means for controlling a rotary speed of a fan motor to a predetermined value by controlling the conducting current signal generating circuit automatically when the power source voltage is elevated over the predetermined rated voltage, an output of the comparator being supplied to the conducting current signal generating circuit.
A still further object of the present invention is to provide a brushless fan motor driving circuit comprising means for detecting a position of a permanent magnet of a rotor, a conducting current signal generating circuit for generating a conducting current signal according to an output of the position detecting means, a conducting current control element for energizing stator windings of the motor according to the conducting current signal, means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a rated voltage when the power source voltage is elevated over a predetermined rated voltage, voltage control means provided between a power source and two stator windings, and means for controlling a rotary speed of a fan motor to a predetermined value by controlling the voltage control means automatically by the output of the power source voltage detecting means when the power source voltage is elevated over the predetermined rated voltage.
A still further object of the present invention is to provide a brushless fan motor driving circuit comprising means for detecting a position of a permanent magnet of a rotor, a conducting current signal generating circuit for generating a conducting current signal according to an output of the position detecting means, a conducting current control element for energizing stator windings of the motor according to the conducting current signal, means for varying a rotary speed of a fan motor, PWM rotary speed instructing means for setting a rotary speed of the fan motor, means for detecting a power source voltage and outputting a voltage in proportion to a difference between the power source voltage and a rated voltage when the power source voltage is elevated over a predetermined rated voltage, and means for controlling a rotary speed of the fan motor to a predetermined value by varying an output voltage the PWM rotary speed instructing means according to an output of the power source voltage detecting means automatically when the power source voltage is elevated over the predetermined rated voltage, the rotary speed varying means comparing a saw-tooth wave signal generated in a saw-tooth wave generating circuit including a time constant circuit consisting of a resistor and a capacitor with the output voltage of the PWM rotary speed instructing means so as to vary an energizing time of the stator windings.
Other object and advantages will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.